#include <stdio.h>
#define exchange(a,b)
{\
    int t;\
    t=a;\
    a=b;\
    b=t;\
}

void main()
{
    int x=10;
    int y=20;
    printf("x=%d;y=%d\n",x,y);
    exchange(x,y);
    printf("x=%d;y=%d\n",x,y);
}

